The present invention generally relates to the field of waveguide filters and, more particularly, to a constricted split block waveguide low pass filter having a printed circuit filter substrate.
One conventional waveguide low pass filter, called a waffle-iron filter, uses longitudinal slots and transverse grooves to define a plurality of metal islands or bosses in the broad waveguide walls to suppress higher order modes. The transverse grooves attenuate the fundamental TE.sub.10 mode; the longitudinal slots suppress the higher order TE.sub.n0 modes. Typically, a waffle-iron filter is designed to suppress up to three times the low-pass filter frequency.
The slots and grooves of the waffle-iron filter are generally cut by machining a metal insert and then bonding the machined insert within the waveguide. A drawback of this conventional waffle-iron filter is that its construction requires high precision machining and thus its cost of manufacture is high.
Consequently, a need exists for a waveguide low pass filter having a low cost design which avoids the necessity for precise and costly manufacturing steps in its construction.